(a) Field of the Invention
The present invention relates to gas turbine engines, and more particularly, to a turbine rotor and an improved blade retention apparatus.
(b) Description of the Prior Art
Turbine rotors are normally constructed with a plurality of individual airfoil rotor blades mounted to the periphery of a rotor disc. Each airfoil blade includes a root that slides into an individual slot formed in the periphery of the disc. In commercial and most military gas turbine engines, it is customary to have individual turbine blades attached to the disc through the use of serrated slots which restrain the blades in the radial and generally tangential directions. In the axial direction however, a separate means of restraint must be provided. For example, the use of a one-piece rivet with a pre-fabricated head at one end and a hollow opposite end which is flared after the blade is commonly used.
Such a method of blade retention presents numerous disadvantages. There have been instances where the rivets have not provided sufficient resistance to the axial loads imparted by the blades and have been allowed to slip out of their serrations and rub against adjacent components. This phenomenon can be attributed to the relatively weak structure which constitutes the flared end of the rivet and due to the assembly process which places the rivet in a residual compression. Attempts to improve the blade retention have resulted in a variety of riveting methods. An orbital riveting machine was introduced to install rivets to the blades. This machine is large, complicated and expensive. Another method that was introduced included placing a hollow rivet by a solid stem with a conical collar inserted at the end of the rivet which was subsequently set with a hydraulic press. This method, although useful, introduced an installation technique which was three times longer than the previously used method.